Watch for Firefox 5 Release in June

If it meets that schedule, Mozilla could crank out Firefox 6 just two months later.

Mozilla has shifted to a faster-paced development cycle where it adds new features as it goes to a series of versions -- dubbed nightly, aurora, beta and Firefox -- each of which feeds into the next-most-stable build until a polished edition is released.

Artwork: Chip TaylorThe change is a major shift for the open-source company, which has been locked into a much longer schedule. Firefox 4, for example, was in development for over a year, while Firefox 3.6 took about the same amount of time to finish.

Google uses a similar process to continually feed features to Chrome, relying on a four-channel line of development: nightly, dev, beta and stable. The result is a new version of Chrome every six to eight weeks.

Mozilla is currently planning a truncated schedule for Firefox 5, which should ship June 21. To meet that deadline, Firefox 5 has to hit the "aurora" channel April 12 and reach beta by May 17.

With Firefox 5 done, Mozilla will shift to a standard 18-week schedule that will put Firefox 6's release around mid-August.

To meet those dates, Mozilla will add features to Firefox as it goes. If a feature is not ready for the first of the four channels -- what the company calls "nightlies" as well as "Mozilla central" -- it will not be added later to the aurora or beta builds. Features with problems will be backed out of an edition -- say Firefox 5 -- and deferred until the next in line.

Google essentially does the same with Chrome.

Mozilla will apparently also stop shipping interim security updates as of Firefox 5, and instead patch vulnerabilities as fixes are crafted, with the final Firefox build given priority.

The only exception will be emergency security updates, which Mozilla calls "chemspills." Those will land simultaneously on all four channels, and result in an emergency update to the beta and release lines.

Ideally, Mozilla's new plan will update the beta channel every week, the nightly and aurora channels every day, and the Firefox build every six weeks.

Key to the new plan is a "silent update" mechanism in Firefox that automatically upgrades the browser to each new version as they're completed. Chrome is the only browser that now updates in the background without notifying the user or requiring any user action.

Mozilla has worked on silent updating on and off for months. Originally slated to ship with Firefox 4 , the feature was pulled from that version last fall. It must now make it into Firefox 5 in order for the rapid roll-out of Firefox 6, 7 and beyond to work smoothly.

Since final Firefox releases will not be held for any single feature, it's impossible ahead of time to know what each version will contain. But Mozilla has posted a long wish list of enhancements and additions that range from a near-term identity manager to a long-range goal of bundling Flash with Firefox.

Al Hilwa, an analyst with IDC, has praised Mozilla's more frequent release plans for Firefox, which he saw as a reaction to Chrome's rapid schedule.

"Chrome's development model has been a successful experiment in terms of getting production releases with improvements and new features out quickly and much faster than in the past," Hilwa said last month. "I think this is causing waves in the industry, most specifically for direct competitors."